Safety device for punch presses



Dec. 20, 19551 a. R ISAAC, JR

SAFETY DEVICE FOR PUNCH PRESSES Filed Sept. 15, 1952 /n ven for George R /s00c,Jt 3

k 8. m 4 fforn ex United States Patent 9 SAFETY DEVICE FOR PUNCH PRESSES George R. Isaac, Jr., Grand Rapids, Mich.

Application September 15, 1952, Serial No. 399,624

4 Claims. (Cl. 74-615) The present invention provides a safety device for a punch press. It is common knowledge that operators of these machines work under the continuing danger of serious injury to their hands and arms due to the possibility of having them caught between the die components as they close with tremendous force. The fast and rhythmic sequence of movements of the punch press operator are such as to tend to establish a pattern which is followed by him unconsciously. After these movements have been mastered, the direct attention of the operator inevitably departs from the details of his work; and it is frequently the case that operators are able to proceed for long periods while having their mind directed to some entirely unrelated subject.

Under these conditions, the matter of the safety for the operators hands, fingers, and arms becomes particularly acute. Since the very nature of his movements is such that it prevents continuing attention being given to the placement of his hands during the operation of the press, much thought has been given to the development of devices that will assure that his hands will be away from the closing area of the dies at the time the press begins its downward stroke. One type of mechanical device (to which the present invention is related) involves a pair of vertically-extending arms pivoted at a point near the upper area of the press. As the press begins its downward stroke, suitable mechanism causes these arms to fly out in the manner of a pair of opening scissor blades. This action will of course knock away any obstruction in the path of travel. While a blow on the arm of an operator from one of these devices is not a pleasant experience, it is undeniably less severe in its consequences than would be the case if the press were to close on his hands or fingers.

The conventional design for this type of device involves a linear cam that is pulled between suitable followers associated with the pivoted safety arms. The arms are biased in the direction of the cam, and the necessary outward snap of the arms is accomplished by a suitably formed surface on the linear cam. It is vital that the outward movement of the arms be well under way at the very earliest possible stages of the downward movement of the c osshead of the press. In view of this requirement, the rate of rise of the cam is usually established at the maximum before unduly large operating forces become involved. it will be noted that the necessity for a rapid outward movement with a small travel of the cam makes the positioning of the arms very sensitive to variations in position of the pivot point of the arms, the surface of the linear cam, and similar points where wear is likely to take place. In view of the high loading caused by the rapid rate of cam rise, this wear problem becomes particularly aggravated. Since the arms confine the linear cam betw en them, the accumulation of tolerances and wear result in the development of lost motion in the arms after a relatively short period of use of the device Improper positioning of the knockout arms amounts to -a failureto properly clear the danger area. g

Another problem encountered in the use of the usual device of this type is the modification of it to suit specific needs. Each punch press is capable of accommodating a large variety of dies, audit is theusual procedure to adjust the travel of the knock-out arms to approximately the full width of the die unit. On particularly large dies, the matter of assuring a full stroke without overloading the unit (in view of the requirement for a rapid cam rise) becomes particularly acute. The difficulty of changing the contour of a linear cam to suit specific needs is obvious, and it is the usual practice to simply adjust the vertical position of the standard unit and the length of the arms to give the necessary stroke. The process of changing the dies in the press is also hindered by the presence of the safety device.

The present invention provides a safety device in which the stroke itself is readily adjustable, rendering unnecessary the continuing variation in vertical position to obtain the necessary swing of the arms. The variation of the stroke of the device contemplated by the present invention is accomplished by a change in the cam itself, the construction being such that the replacement of these cams is a very simple operation. The working parts are mounted on this device in such a manner that each of the arms, and the cams directly associated therewith, are supported as independent units. With this arrangement, the effect of wear upon each of these portions of the device does not tend to accumulate and thereby have as great a tendency to render inaccurate the positioning of the arms. The mounting structure of the knock-out arms of the present invention provides for adjustably moving them to a non-functioning position giving clearance for changing dies in the press.

The features of the present invention will be discussed in detail through an analysis of the particular embodiments illustrated in the accompanying drawings. In these drawings:

Figure 1 illustrates a side elevation of a punch press equipped with a device constructed according to the present invention.

Figure 2 is a section taken on the plane 2-2 of Figure 1.

Figure 3 is a view similar to Figure 2, but showing the knock-out arms of the device in the open position after the stroke of the press is under way.

Figure 4 is a section taken on the plane 4-4 of Figure 3.

Referring to Figure l, a punch press 10 is shown provided with the conventional 6 frame 11 and a base 12. The attitude of the frame is adjustable by the conventional construction including the arcuate slot 13 and the pivot bolt 14. Securing the bolt 15 at various positions along the slot 13 will serve to rotate the frame 11 to various angular attitudes with respect to the vertical to give the necessary plane of action of the die components 16 and 17. The lower component 17 is secured to a plate 18 which is fixed with respect to the frame 11. The upper component 16 is fixed with respect to the crosshead 19, having the characteristic reciprocating motion induced by a connecting rod and crank system associated with the shaft 24 and the driving wheel 21.

The safety device generally indicated at 22 in Figure l is preferably mounted upon the projections 23 that are conventionally provided on the frame 11 to accommodate tie rods when increased stiffness of the 0 frame 11 is necessary. The safety device is essentially a mechanism for actuating the knockout arms 24 and 25 with an outwardly-snapping motion extending approximately the width of the die which may be mounted in the press. A base plate 26 is provided with the angle brackets 27 and 28 adapted to be secured to the projections 23. The mounting arms 29 and 30 are mounted on the pivot studs 31 and 32 respectively, the studs being firmly secured to the base plate 26. It may be noted that the base plate 26 is shownin front of the operating mechanism mounted on it. This arrangement may be reversed, if desired;

when access to the working parts is of primary importance. It is conventional practice to form the knock-out arms 24 and 25 of wood; and accordingly, the clamps 33 and 34 are provided on the arms 29 and 30. The clamps 33 and 34 have split ends, and grip the arms 24 and 25 under the urging of the bolts 35 and 36. The clamps 33 and 34 are adjustable about a horizontal axis on the arms 29 and 30. It is therefore possible to loosen the locking nuts 37 and 38, and to rotate the arms outwardly from the press during the installation of various dies. This adjustment makes it unnecessary to remove the entire unit from the press, as is often the case with devices known to the prior art.

The mounting arms 29 and 30 are each provided with a roller 39 and 40, respectively, which is disposed in a common plane with the cams 41 and 42. Referring to Figure 4, the cams 41 and 42 are mounted on the shafts 43 and 44, and are in driving engagement with the gears 45 and 46, respectively. The engagement of the cams 41 and 42 with the gears 45 and 46 is preferably through the medium of a non-circular hole. A forced fit is not desirable in view of the necessity of changing the cams 41 and 42 to establish various lengths of stroke of the arms 24 and 25. The replacement of the cams 41 and 42 is easily accomplished through the removal of the nuts 47 and 48.

The gears 45 and 46 are driven by the sliding rack 49. The path of this rack is established by the guide block 50 which is secured to the base plate 26 by screws as indicated at 51 in Figure 4. Referring to Figure 3, the downward movement of the rack 49 causes the gears 45 and 46 to rotate, and brings the recesses 52 and 53 of the cams 41 and 42 away from the position illustrated in Figure 2. The rollers 39 and are therefore forced to ride upon the outer periphery 54 and 55, respectively, this condition corresponding to the outer position of the arms 24 and 25. A spring 56 connecting the mounting arms 29 and 30 serves to bias them together, and return the arms 24 and 25 to the position shown in Figure 2 after the press has returned with the crosshead near the uppermost part of its stroke.

The operating connection between the rack 49 and the crosshead of the press in provided through the arm 57 secured to the rack 49, and the turnbuckle 58 connecting the arm 57 to the crosshead 19. It is preferred that the turnbuckle 58 be connected to a member 59 projecting from the crosshead 19, and variation of the length of the crank arm of the press is compensated for by corresponding adjustment of the turnbuckle 58. With this arrangement, the length of the rack 49 must accommodate the stroke of the press, and the relationship between the rack 49 and the gears and 46 should be established so that the press stroke does not bring the recesses 52 and 53 around a full 360 degrees. If a positive stop on the rack 49 does not permit movement equal to the stroke of the press, a resilient connection should be provided between the rack and the crosshead, together with a return spring on the rack.

The particular embodiments of the present invention that have been illustrated and described herein are for illustrative purposes only and are not to be considered as a limitation upon the scope of the appended claims. In these claims, it is my intention to claim the entire invention disclosed herein except as I am limited by the prior art.

I claim:

1. A safety device for a punch press, said punch press having a frame and a reciprocating crosshead, comprising: a base plate adapted to be mounted on said frame in a plane parallel to the movement of said crosshead; a rack member slideably mounted on said frame for movement in a direction parallel to the movement of said crosshead, said rack member having teeth on the opposite sides thereof perpendicular to said base plate; gear means rotatably mounted on said base plate on opposite sides of said rack 4 member and engaging said teeth; cam means rotatably mounted on said base plate for rotation on an axis fixed with respect thereto and driven by each of said gear means; knock-out arm meanspivotally mounted on said base plate on opposite sides of said rack member, said knock-out arm means each having cam-follower means engaging the adjacent of said cam means; biasing means urging said knock-out arm means together; and tension means connecting said rack member to a point fixed with respect to said crosshead.

2. A safety device for a punch press, said punch press having a frame and a reciprocating crosshead, comprising: a base plate adapted to be mounted on said frame; a rack member slideably mounted on said frame for movement in a direction parallel to the movement of said crosshead, said rack member having teeth on the opposite sides thereof perpendicular to said base plate; gear means rotatably mounted on said base plate on opposite sides of said rack member and engaging said teeth; cam means rotatably mounted on said base plate for rotation on an axis fixed with respect thereto and driven by each of said gear means; knock-out arm means pivotally mounted on said base plate on opposite sides of said rack member, said knock-out arm means each having cam-follower means engaging the adjacent of said cam means, said knock-out arm means also having a lockable joint providing adjustable positions of a portion of said knock-out arm means in a plane parallel to the axis of the pivotal mounting of said knock-out arm means; biasing means urging said knock-out arm means together; and tension means connecting said rack member to a point fixed with respect to said crosshead.

3. A safety device for a punch press, said punch press having a frame and a reciprocating crosshead, comprising: a base plate adapted to be mounted on said frame; a rack member slideably mounted on said frame for movement in a direction parallel to the movement of said crosshead, said rack member having teeth on the opposite sides thereof perpendicular to said base plate; gear means rotatably mounted on said base plate on an axis fixed with respect thereto and on opposite sides of said rack member and engaging said teeth; cam means removably mounted coaxially and in driving engagement with each of said gear means; knock-out arm means pivotally mounted on said base plate on opposite sides of said rack member, said knock-out arm means each having cam-follower means engaging the adjacent of said cam means; biasing means urging said knock-out arm means together; and tension means connecting said rack member to a point fixed with respect to said crosshead.

4. A safety device for a punch press, said punch press having a frame and a reciprocating crosshead, comprising: a base plate adapted to be mounted on said frame; a rack member slideably mounted on said frame for movement in a direction parallel to the movement of said crosshead, said rack member having teeth on the opposite sides thereof; gear means rotatably mounted on said base plate on opposite sides of said rack member and engaging said teeth; cam means rotatably mounted on said base plate for rotation on an axis fixed with respect thereto and driven by each of said gear means; knock-out arm means pivotally mounted on said base plate on opposite sides of said rack member, said knock-out arm means each havingcamfollower means engaging the adjacent of said cam means; biasing means urging said knock-out arm means together; and tension means connecting said rack member to a point fixed with respect to said crosshead.

References Cited in the file of this patent UNITED STATES PATENTS 511,014 Hagelstein Dec. 19, 1893 1,301,567 Jelsema Apr. 22,1919 1,358,528 Danks Nov. 9, 1920 1,393,510 Dubisky Oct. 11, 1921 2,347,606 Miller Apr. 25, 1944 

